Summary
The FAA is revising an earlier proposed airworthiness directive (AD) for certain Boeing Model 777-200 and 777-300 series airplanes. The original NPRM would have required repetitive inspections for discrepancies of the splined components that support the inboard end of the inboard trailing edge flap; related investigative, corrective, and other specified actions if necessary; a one-time modification of the inboard support of the inboard trailing edge flap by installing a new isolation strap and attachment hardware; and repetitive replacement of the torque tube assembly. The original NPRM resulted from reports of corrosion on the torque tube and closeout rib fittings that support the inboard end of the inboard trailing edge flap, as well as a structural reassessment of the torque tube joint that revealed the potential for premature fatigue cracking of the torque tube that would not be detected using reasonable inspection methods. This action revises the original NPRM by providing the terminating action for the repetitive inspections of modifying the inboard main flap. This action also revises the original NPRM by specifying prior or concurrent accomplishment, for certain Boeing Model 777-200 series airplanes, of one-time inspections of the flap seal panels for cracking and minimum clearances, and of the torque tubes for damage; and related investigative and corrective actions if necessary. We are proposing this supplemental NPRM to detect and correct corrosion or cracking of the torque tube and closeout rib fittings that support the inboard end of the inboard trailing edge flap. Cracking in these components could lead to a fracture, which could result in loss of the inboard trailing edge flap and consequent reduced controllability of the airplane.